In the bloodstream, which cell type serves as the immediate precursor to macrophages?

In the bloodstream, which cell type serves as the immediate precursor to macrophages?

• A. Neutrophil
• B. Monocyte
• C. Lymphocyte
• D. Erythrocyte

Answer: (B)

Monocytes circulate in the blood as the immediate precursor to macrophages. When they exit the bloodstream and migrate into tissues, they differentiate into macrophages, the long-lived phagocytes that engulf pathogens and debris. Neutrophils are a separate, rapidly responding phagocyte that do not become macrophages. Lymphocytes come from the lymphoid lineage and are involved in adaptive immunity, not macrophage formation. Erythrocytes are mature red blood cells arising from the erythroid lineage and do not differentiate into macrophages. Thus, the circulating monocyte is the precursor to macrophages.

Monocytes circulate in the blood as the immediate precursor to macrophages. When they exit the bloodstream and migrate into tissues, they differentiate into macrophages, the long-lived phagocytes that engulf pathogens and debris. Neutrophils are a separate, rapidly responding phagocyte that do not become macrophages. Lymphocytes come from the lymphoid lineage and are involved in adaptive immunity, not macrophage formation. Erythrocytes are mature red blood cells arising from the erythroid lineage and do not differentiate into macrophages. Thus, the circulating monocyte is the precursor to macrophages.